1. Field of the Invention
This invention relates to power supplies and more particularly relates to increasing the efficiency of power supplies with multiple power outputs.
2. Description of the Related Art
A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electrical or other types of energy to a load or group of loads. A power supply, in some embodiments may be configured to convert power in one form to another form, such as converting alternating current (“AC”) power to direct current (“DC”) power. The regulation of power supplies is typically done by incorporating circuitry to tightly control the output voltage and/or current of the power supply to a specific value. The specific value is typically closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input.
For example, in an electronic device such as a computer, the power supply is typically designed to convert an AC voltage input such as is traditionally provided by a conventional wall socket, into several low-voltage DC power outputs for transmission to the internal components of the electronic device. Conversion is typically performed in stages that may include various stages such as a rectification stage, a pre-regulation stage such as an active harmonic filter, a regulator/chopper stage, etc. The stages may be configured in various topologies such as a boost stage, a buck stage, or other derivative topology.
In addition to providing main power outputs to various electronic devices, power supplies are often configured to provide auxiliary and standby power to background systems and sub-systems within an electronic device. For example, even when an electronic device is not fully operational, or is turned off, power may still be needed to power system clocks, system controllers, system monitors and the like. Conventional power supplies typically include several stages of power conversion in order to provide main power as well as standby and auxiliary power. In some embodiments, the power supply itself may require auxiliary power to run the control and drive circuits within the power supply. In a common system, a main output voltage of 12 volts may be generated. Additional 5 volt and 3.3 volt auxiliary voltages may be derived from the main output voltage by implementing additional conversion stages, which can be expensive to implement and which decrease the efficiency of the power supply.
For example, in a power supply that provides a 12 volt main output voltage, a DC to DC regulator may be utilized to convert the 12 volt output to a 3.3 volt output to provide power to standby circuits. The additional DC to DC regulator results in a significant additional power loss and can be costly to implement. This embodiment is inefficient because inefficiencies are compounded where the power is converted multiple times and losses occur at each stage. In some embodiments, several additional DC to DC regulators may be required to generate additional voltage levels that may be needed in the auxiliary and standby circuitry. The net result of such conventional methods of providing standby and auxiliary power is that the overall efficiency of the power system is lower and the cost is higher.
Thus, most multistage power systems do not have a very high overall efficiency due to loss of power in each stage. For example, if the efficiency of the first stage is 96%, second stage is 90%, and third stage is 87%, then the overall efficiency of the circuit is only 75%. The result is an overall loss of efficiency.